State ur observation whrn dil.hydrochloric acid is added to magnesium ribbons
Magnesium ribbon is just another form of magnesium metal. This reacts with hydrochloric acid (and virtually all other acids) to form the acid salt of magnesium and hydrogen:
Mg + 2HCl = MgCl2 + H2
Hydrogen is a gas and will be seen as bubbles. However, it is also very explosive, so do not have any flames around when you do it, unless you know exactly what you are doing! Magnesium chloride is soluble, so the magnesium ribbon will slowly disappear into solution.